Battery Enclosure Overview
- Shem Kim
- Nicole Choe
The Enclosure is where our main battery pack, auxiliary battery, BMS boards, and the DCDC board is contained. We are aiming to finish manufacturing of the enclosure by the end of the Fall 2023 term.
Timeline for Fall 2023 Manufacturing:
(insert updated gantt chart here)
Design Requirements & Considerations
The design of the enclosure is based on the following main requirements:
ASC Regulations
Impounding (8.10)
General enclosure regulations (8.4)
Ventilation
Security
Mounting to chassis
Electrical shock safety (8.9)
Battery pack cooling (prevent overheating)
Ease of removability
Size (must fit in chassis)
Weight (minimize)
Integration with overall pack and boards inside
Most of the requirements are pretty straight forward, we need cooling because overheating batteries can cause thermal runaway, which is when the battery chemistry gains enough energy that it starts reacting uncontrollably.
Gets too hot → chemical reactions occur → heat is generated from reactions → gets hotter → more chemical reactions occur → more heat is generated → as this is occurring, cells are on fire and car is on fire
Figure 2: Thermal Runway of the battery of a car (we don’t want this)
We need to consider the ease of removability because we might have to take the box out to troubleshoot boards, replace modules, replace aux battery, and other troubles that may arise during the race. For example, if a single cell in a module becomes non-functional, we have to replace the entire module, and the enclosure is hard to reach while it is in the chassis.
Size and weight are important constraints to consider because we need to make sure our box actually fits into the space the chassis provides, and it also needs to be as light as we can make it so that the weight of the box doesn’t mess with the center of mass of the car and also because more weight means more energy needed to move the car.
ASC regulations is more than just impounding and safety but those were the main ones we kept in the back of our minds while designing. Safety is just to make sure our box doesn’t separate from the car due to a crash or a roll-over (though the design of the car and ASC regulations make it impossible for a roll-over to occur anyway). Impounding is a rule that makes it so that the batteries are not accessible from outside of the box. This rule is in place to prevent teams from secretly replacing their modules with fully charged ones or from secretly charging the batteries from an external source. The event gives 4 of these seals shown in Figure 3, which is used to “lock” the box and make it impossible to access without breaking the seals (which can only be done with permission from the organizers and will be monitored, probably).
Design
The full dimension of the box is 693.25 x 400 x 235 (mm). The box itself is made up of fiberglass panels attached to an aluminum frame. On the front and back are going to be two 120mm x 120mm Noctua IPPC NF-F12 3000 PWM fans for cooling the modules.
The box sits on four steel flats and is also bolted to two more flats on the front and back to prevents lateral movement.
The modules will sit as shown in Figure 6, the CAD does not yet show the electrical components like the BMS boards that need to be attached to the modules (BMS in simple terms helps manages all the batteries' performance). The modules shown in Figure 6 below are not the complete versions either, partly because rendering the full modules with every single cell takes a toll on my computer, but the figure below is enough to get the idea across.